HP Fortran Programmer's Reference (September 2007)

Arrays

Array declarations

Chapter 364

Allocatable arrays

An allocatable array is a deferred-shape array with the ALLOCATABLE attribute. Its bounds

and shape are deﬁned when it is allocated with the ALLOCATE statement. Once allocated, the

allocatable array may be used in any context in which any other array may appear. An

allocatable array can also be deallocated with the DEALLOCATE statement.

An allocatable array has an allocation status that can be tested with the ALLOCATED intrinsic

inquiry function. Its status is unallocated when the array is ﬁrst declared and after it is

deallocated in a DEALLOCATE statement. After the execution of the ALLOCATE statement, its

status is allocated. An allocatable array with the unallocated status may not be referenced

except as an argument to the ALLOCATED intrinsic or in an ALLOCATE statement. If it has the

allocated status, it may not be referenced in the ALLOCATE statement. It is an error to allocate

an allocatable array that is already allocated, or to deallocate an allocatable array either

before it is allocated or after it is deallocated.

In HP Fortran, an allocatable array that is unallocated, is local to a procedure, and does not

have the SAVE attribute. It is automatically deallocated when the procedure exits.

The following example, alloc_array.f90, calls a subroutine that allocates and deallocates an

allocatable array and uses the ALLOCATED intrinsic function to test its allocation status:

Example 3-1 alloc_array.f90

PROGRAM main

! driver program for calling a subroutine that allocates and

! deallocates an allocatable array

CALL test_alloc_array

END PROGRAM main

SUBROUTINE test_alloc_array

! demonstrate how to allocate and deallocate an allocatable array

! the array matrix is rank-2 allocatable array, with no

! shape or storage

REAL, ALLOCATABLE, DIMENSION(:,:) :: matrix

INTEGER :: n

LOGICAL :: sts

! sts is assigned the value .FALSE. as the array is not yet

! allocated

sts = ALLOCATED(matrix)

PRINT *, 'Initial status of matrix: ', sts

PRINT *, 'Enter an integer (rank of array to be allocated):'

READ *,n

! dynamically create the array matrix; after allocation, array